Shaft Sinking … getting down to the opal level
Shaft Sinking by Hand
In the 1960s miners started using power tools to assist in breaking up the sandstone to sink their shafts. Jackhammers driven by air from compressors allowed much greater quantities of rock to be broken up compared with using a pick, but this rock then had to be shovelled into a bucket and lifted to the surface by a miner operating a windlass.
In some opal fields a hard surface layer of silcrete made digging shafts very hard work. Miners would drill a circle of blast holes using a small auger then pack these with explosives to blast and break up the hard layer.
Calweld Drill Rigs
The California Welding Co. in the USA produced large diameter drill rigs with teeth around the bottom of a heavy cylindrical steel bucket. As the drill rotates, the teeth cut into the rock below, breaking it up and forcing lumps into the bucket which has a flap underneath to hold the dirt while it is raised to the surface. At the surface, the bucket is swung away from the shaft collar using a winch before the flap is opened to release the dirt.
When several of these drill rigs were brought to the opal fields in the 1970s they became the preferred method for shaft sinking.
Some miners who could afford to purchase the rigs, and who also had the skills to operate and maintain them, became shaft sinking contractors.
The first diggers developed for underground mining were too large to fit down the shafts made by the three-feet diameter Calweld drills. Larger shafts, up to seven feet in diameter, were made by enlarging the three-feet shaft with a reamer – an arm attached to the drill bucket with teeth that broke up the rock around the shaft.
Percussion Drills and Large Auger Drills
In areas where there are layers of hard silcrete, Calweld drills are slow and need frequent repairs to maintain the cutting surfaces. In these mining fields some miners use percussion drilling rigs which can sink holes more rapidly in hard rock. Large auger drills have also been used – in some conditions they can drill faster and are easier to operate and maintain.
The extent of mining in the clay levels of a mine was often limited because of the difficulty of providing ventilation to remove hot air and dust at the end of a long drive. After the introduction of auger drills for prospecting in the 1980s miners could quickly drill ventilation shafts down to the longest drives to allow more air circulation.